It is common practice to intermittently feed strip material by means of a sprocket which has teeth which engage spaced-apart index holes in the strip. The sprocket is intermittently rotated by a stepping motor or the like so that the strip is fed during periods of rotation of the sprocket and the strip is not fed when the motor is not energized. It is necessary, in feeding devices of this type, to provide a guide member extending tangentially with respect to the sprocket to hold the strip material in engagement with the sprocket.
In feeding devices of the type described above, and for that matter, in most known feeding devices such as hitch feeds, it is difficult to avoid a slight amount of chattering or other strip movement at the end of the feeding interval and the strip is, moreover, firmly constricted or held by the sprocket after it comes to rest. This characteristic is undesirable in many stamping and forming machines for the reason that the stamping and forming die assembly usually has pilot pins which enter the index holes in the strip at a location adjacent to the feeding device and precisely position that portion of the strip which extends through the stamping die. If the strip is tightly held against longitudinal movement by the feeding device, and if the pilot holes in the vicinity of the die are not precisely aligned with the pilot pins, the portion of the strip extending through the die might be damaged when the punches and dies subsequently engage the strip. This can be particularly damaging if the strip has previously been partially formed or if the blanks have been punched from the strip. The pilot holes will fail to precisely align the partially formed strip material with the punches and dies and damage to the partially formed parts or to the blanks in the strip will result. It would be desirable to release the strip at the instant of the end of the feeding interval from the feeding device so that the pilot holes could center the strip in the die by causing it to move a very slight amount as they enter the index holes in the strip. The distances being considered here are, of course, very slight, of the order of 0.001 inches, but a misalignment of even this slight amount can result in the production of inferior parts which may not satisfy the tolerance specifications for the parts being manufactured.
The present invention is directed to the achievement of an improved sprocket type feeding mechanism which can be precisely controlled as is required for high-speed stamping and forming operations and which, at the conclusion of each feeding interval, releases the strip material so that it can be moved in the direction of its length by a very slight amount when the pilot pins in an adjacent die enter the index holes of the strip. The invention is also directed to the achievement of an improved bell crank type mechanism which is used in the practice of the present invention and which can be used for other purposes.